No, I don't mean it isn't there at all. I mean that the reader isn't aware of individual words or sentences, but instead absorbs the message that they were written to convey.
That need for invisibility is one of the reasons why it's so important to proofread for typos, misused words, and misspellings. They're like big stop signs – or at least speed bumps – in the copy. They interrupt the flow by forcing the reader to stop and focus on the words themselves. Then the magic of the message is gone.
Of course, that's only one reason to avoid using copy filled with typos and misused or misspelled words. The other reason is that errors show a lack of attention to detail – and that's not a trait most people want in their real estate agent.
Invisibility is also the reason why copywriters strive to keep the language at about a 7th grade reading level and to avoid industry jargon. We don't ever want to cause a reader to stop and think "What does that word mean?"
Think of it like the picture window through which you can gaze on a breathtaking view... you don't "see" the window unless it's cracked or dirty. If it's clean and doing it's job, all you're aware of is that view.